Copine-I represses NF-κB transcription by endoproteolysis of p65

Nuclear factor-KB (NF-KB) is a dynamic transcription factor that regulates important biological processes involved in cancer initiation and progression. Identifying regulators that control the half-life of NF-KB is important to understanding molecular processes that control the duration of transcriptional responses. In this study we identify copine-I, a calcium phospholipid-binding protein, as a novel repressor that physically interacts with p65 to inhibit NF-KB transcription. Knockdown of copine-I by siRNA increases tumor necrosis factor α-stimulated NF-KB transcription, while copine-I expression blocks endogenous transcription. Copine-I abolishes NF-KB transcription by inducing endoprotease processing of the N-terminus of p65, a process antagonized by iκBα. Copine-I stimulates endoproteolysis of p65 within a conserved region that is required for base-specific contact with DNA. p65 proteins lacking the N-terminus fail to bind to DNA and act as dominant-negative molecules that inhibit NF-KB transcription. Our work provides evidence that copine-I regulates the half-life of NF-KB transcriptional responses through a novel mechanism that involves endoproteolysis of the p65 protein.